Configuration for postfix and courier

I can see SquirrelMail from a browser. When I log in to SquirrelMail my mail.info shows a successful login but the browser shows:
ERROR: Connection dropped by IMAP server.
Query: SUBSCRIBE "INBOX.Sent"

Now... if I go to to browse the mail folder, I get this:
mark@linux800:/var/mail/virtual/mark$ ls -a
. .. .Drafts .Sent .Trash
mark@linux800:/var/mail/virtual/mark$

I created the 'mark' folder in virtual, and assigned virtual as the group and owner.

Now... the HowTo said something about things running chrooted, and this could cause a problem with Debian based distros (Ubuntu is Debian based). Could this be the problem, that Courier can't do what it needs with file/folder access?

I've also tried Evolution to connect, but I'm assuming that if I can't subscribe via telnet, no other client can either. But I did also try Evolution using POP, and that failed.